Plasma processing is a technique essential for manufacturing semiconductor devices. In recent years, due to an increasing demand for high-integration and high-speed of the LSIs (Large-Scale Integration circuits), there have been efforts to miniaturize semiconductor devices constituting LSIs. Accordingly, there is a need for a plasma processing apparatus to cope with such miniaturization of semiconductor devices with LSIs.
However, in a conventional parallel plate type or inductively coupled plasma processing apparatus, semiconductor devices are damaged by plasma due to high electron temperature of generated plasma. Further, since a region having high plasma density is limited, it is difficult to perform uniform and high-speed plasma processing for semiconductor wafers with LSIs.
In this regard, an RLSA (Radial Line Slot Antenna) microwave plasma processing apparatus is proposed to uniformly generate a high-density surface wave plasma having a low electron temperature.
The RLSA microwave plasma processing apparatus generates a surface wave plasma by using a microwave and processes target objects by using the surface wave plasma. In the RLSA microwave plasma processing apparatus, a radial line slot antenna, i.e., a planar slot antenna having a plurality of slots formed therein with a predetermined pattern, is provided in the upper portion of a chamber as a microwave radiation antenna, and a microwave guided from a microwave source is radiated into the chamber kept at vacuum through the slots. Further, a dielectric microwave transmission plate provided below the slots. By an electric field of the microwave, a surface wave plasma is generated in the chamber and target objects such as semiconductor wafers are processed by the plasma.
However, in the RLSA microwave plasma processing apparatus in which the microwave is introduced from a ceiling wall of the chamber, it may be difficult to control a gas flow if a processing gas is supplied from a gas inlet provided in a side wall of the chamber, which may result in insufficient plasma uniformity.
In order to avoid this problem, there has been proposed a technique in which a dielectric member having a plurality of gas holes is placed under the radial line slot antenna as a shower plate and a processing gas is introduced into a chamber via this shower plate. This technique may allow the processing gas to be uniformly supplied to a space immediately below the shower plate, thereby providing uniformly formed plasma.
However, the aforementioned technique may cause a problem of converting the processing gas within a gas space of the shower plate into a plasma, which may result in a loss of microwave power and an occurrence of abnormal discharging.
In order to solve this problem, there has been proposed a configuration in which a cover plate made of dielectric material having a relative dielectric constant lower than that of the shower plate is interposed between a microwave antenna and the dielectric shower plate. This configuration reduces a variation in relative dielectric constant of the shower plate including the gas space, which may result in prevention of power loss and abnormal discharging in the gas space of the shower plate.
However, since the shower plate is still a dielectric, the aforementioned configuration cannot fully prevent gas in the gas holes formed in the shower plate from converting into a plasma by the microwave transmitting the shower plate, which may still result in power loss and abnormal discharging. However, a technique for forming a uniform plasma while avoiding this problem has not yet been realized.